Shale oil refining



Dec. l5, 19.53 R. c. cAsTNER ETAL SHALE OIL REFINING Filed May 25, 1951 Pafentecl Dec. 15, 1953 smitsI oIL REFININGe Robert C. Castner and Raymond C. Archibald, Berkeley; Calif., a'ssignors to Shell Development;- Company, Emeryville, Calif.,. a: corporation of Delaware Application vMay 25,1951,1 Serial No; 228,302

4' Claims. l

Ihis invention relates to the reiining of. shale oil. More particularly, theinvention relates to a method for improvingy the characteristics of' charging stocks from shale oil for use in catalytic cracking processesl while minimizing the loss of suitablecracking material.

ShaleV oil as produced from oil shale contains on'lya minor proportion of materials which are suitable for use directly inv motor fuels without prior chemical conversion thereof. It is essential, therefore; that the shalel oil, for the most part, be subjected to conversion processes'oi the general character used for increasing.. the yield and quality of motor fuels derivable from heavy4A crudeY oils; However., aserious drawbackxtoy the useof shale oil for. the production ofmotor fuels" therefrom by catalytic processing isA the.. large amount of'coke' formed when the oil is subjectedY to catalytic' cracking; A

Shale oil as` produced from Colorado oil'shale` by theusual'retorting processes, suoliA as the so calledN-T-U retorting process, is a black.' heavy waxy oil with an API'gravity of' about 20' anda pour point of around 90` F.containing about 2% by Weight nitrogen, 1%' sulfur'and 1% Oxy'- gen, and having alow'naphtha content, usually less than 3%.. Only 20`25% ofthe oil is ali'- phatic and perhapsalicyclic `as well and probably at least 25% is aromatic inY character;, the remainder is accounted for by compounds containing nitrogen, suliur, and oxygen. A repre# sentative sample of N-T-U shale oil produced at the Rifle, Colorado, demonstration plant ofthe' U. S. Bureau of Mines had the following approximate analysis expressed as Weight per' cent': C'-84.5, ifi- 11.5, N-1.9', Sl-0.8,'v and O-'-1'.3`. Fromfthisanalysis, it Will be'noted thattheV shale oil contains more nitrogen and. oxygen 'than most petroleum and hasan H: C' atom ratio" corre#- spending approximately to a California straight run longv residue.

Many of the problems associated with the' renning of.. shale oils, and various methods proposed and usedhave been discussed inconsid erable detail" in a report ofthe Bureau ofMines,`

Report of Investigations 4652, Synthetic Liquidy Fuels, Part I-Oil from Oil Shale,y February 1950. Thus, it is stated therein. that gasoline of good octanerating canbe made by catalytic cracking of shale-oil'factcns, butcoke forma- 'l 2 tion on thefcatalyst causes a= short catalystlife. Attributing the high.- coke l formation to the presence ofl organic nitrogen' compounds,y and: observ-l ing` that the heavy gas-oily fraction. from` shale oil. eductedin anl.\T-'I-Ul retort-.was founditofcon* tainJ more than 4G. percent nitrogen. compounds..r it was indicated that solution to thel problem should belsought forin the developmentof catalysts whicharemoreasuitable'for this applicationi It has already.l been'pointed out'thatit-'is advantageous tosubjectthe/shale oil, because of-itsf highv-iscosityto a thermal-treatmentfor reductionofpour pointlprior to any refining thereof. ThusA far, largescale. operations on. refining of shale oil have been directed primarily tothermalprocessing, including visbreaking, thermal ook-ing, andthe like-,separationof distillate fractions-and removing tarv acids from the distillate fractions by caustic extractionl and removing tar bases from thev caustic-treated. distillate fractions by-r sulfuric acid extraction. It-will be clear from the results offprevious Work onthe refining of shale oil' that many` problems still exist and require so'- lution beforev the most economical-utilization. of shalev oil. can.. be made.

Considerable Work has been done iny anv at-4 tempt to separatek undesirable from desirablev components oi shaleoil by extraction with liquid dioxide,faswell\as the usual well knownorganc selective-7 solvents, y lacks the f required selectivity; Liqueed.- ammonia had too loWf a solubilityvr for the nitrogen compoundsy Certain strenge acids;

for: example;.96% wt. I-IzSOi--torthe` amount ctl00- lbs.y HiSOi/bbliof shale gasoil yielded a raf-v natezcontaining only. 0.1% wt. nitrogen;` The yiel'dloi rafiinat'e lwas about 54 %"Wt. ofthe gasoill butthe' extract could only be recoveredby'springing the nitrogen'compounds with caustic.' Weak' acids such' asssulfurous and'carb'onc acidsliav'e been found :to 'beonly slightly more eiectivefthan Water: Anhydrous'hydroiluoric` acid, although aA relativelyweak' acid, has been foundf toV yield arafiinatecontaining only 013% nitrogen; however, other substanceswere also extracted -to such an extent that the rafnate yield was low. Fur- 3 thermore, removal of all of the iiuorine from the oil is difficult.

It is a principal object of this invention to provide an improved method for the production of improved products from shale oil.

Another object of the invention is to produce from shale oil, feed stocks of improved quality for conversion thereof into motor fuels.

Still another object is to produce from shale oil, feed stocks of improved quality for catalytic conversion thereof into motor fuels while minimizing the lossof suitable cracking material.

The foregoing objects will be better understood, and other objects Will become apparent, from the description of the invention, which will be made with reference in part to the accompanying drawing, the sole gure of which is a process diagram representing a preferred method of carrying out the invention.

Now, in accordance with the present invention, it has been found that shale oil, preferably after having been mildly thermally cracked to lower the viscosity and pour-point substantially, as by a mild visbreaking operation, is effectively sepa-rated by solvent extraction with formic acid under certain conditions, as will be discussed hereinafter, whereby substantially a minimum of the nitrogen-containing compounds, yet representing essentially all of the more undesirable coke-forming nitrogen-containing compounds, are separated in the extract and a maximum amount of good quality cracking stock is separated as rafnate.

In accordance with the invention, there is no attempt made to extract all, or even substantially all, of the nitrogen-containing compounds. To do so would unnecessarily greatly lower the quantity of material obtainable as feed stock for cracking operations for the production of motor fuel. Thus, the method of this invention effects a selective removal of the undesirable coke-forming materials.

In the removal of the deleterious and undesirable materials fiom the shale oil, including certain nitrogen-containing compounds, in the practice of the present invention, it is not known to what extent those compounds are removed simply by physical solution in the formic acid and to what extent they are removed by chemical reaction with forniic acid and the dissolving of the resulting thermally unstable reaction product in the formic acid. Thus, it has been found that as the proportion of formic acid used is increased up to the amount corresponding to about two stoichiometric equivalents of formic acid for each atomic proportion of nitrogen in the oil (about 0.1 volume of 90% formic acid per volume of oil, i. e., about by volume) the proportion of separated raffinate oil phase and the percentage of nitrogen remaining in said rafiinate decrease together. But, as the amount of formic acid used for the extraction is increased further, the amount of raiinate oil remains essentially constant, whereas the nitrogen content of the raffinate oil continues to decrease and at the same time the quality of the rainate oil as catalytic cracking feed stock is improved still further. It has been found further, however, that the quality of the raffinate oil as cracking feed stock is not iinproved still further to any appreciable extent by extracting with a still larger' proportion of formic acid after the nitrogen content of the raiiinate has been reduced to a Value of about Ofi-0.5% by weight, which is obtainable by extraction of the visbroken shale oil with about an equal volume of TABLE I Etractz'on of thermally treated, filtered gras ow shale oil with formz'c acid i Vol. RatimAcid/OL 4/100 6/100 8/100 10/100 20/100 l0/100 Percent N iii Raffinatc Layer 1.80 1. 45 1.23 1. 09 1. 08 0.74 Raiiiiate Layer, I i

percent v Oil 70 61 58 54 l 53 53 To determine the suitability of the raffinate as a catalytic cracking stock, a representative formic acid raffinate from thermally treated N-TU oil, which had a nitrogen content of 0.74% by weight, was subjected to laboratory catalytic cracking at 540 C. at a liquid hourly space velocity of 0.74, over a commercial silica-alun'iina catalyst of 84. square meters per gram surface area, with the production of products in the following weight percentages, based on the weight of feed: sas- 27% gasoline-32% gas oil--29%; coke-i2.2%. For comparison, a railinate was prepared from the same thermally treated N-T-U cil, having a nitrogen content of only 0.14% wt. When this rafnate is subjected to the saine catalytic cracking conditions the results are essentially the same, with no advantage being gained for the additional expense of reducing the nitrogen content to the lower value.

The nitrogen content of the rainnate oil obtained in the extraction depends not only on the proportion of formic acid used, expressed as formic acid, but also on the ratio of formic acid to water in the formic acid solution. rlDhus, whereas an equal volume of 90% formic acid extracts a visbroken shale oil to a raflinate having a nitrogen content of dfi-0.5% by weight, extraction with an equal volume of 52% aqueous formic acid yields a raffinate oil having a nitrogen content of 0.8-0.9% by weight. Nevertheless, the raffinate oil having a nitrogen content of Oil-0.9% is a suitable stock as feed to a catalytic cracking operation. Extraction with about six-tenths of a Volume of 90% forniic acid (saine hydrogen formate pioportion as in one volume of 52% forinic acid) per volume of oil yields a raffinate oil having a nitrogen content of about (2 5-0.6% by weight.

The use of at least an amount of formic acid which corresponds to about 10% by volume of 90% formic acid, and which is essentially two stoichiometric proportions of forrnic acid per each nitrogen atomic proportion in the oil, representing a substantial excess of formic acid on the basis of nitrogen separated in the extract, has been found to be required in order that the extract phase will be sufficiently uid for ready scparation from the raffinate phase. With up to about 10% by Volume of 90% formic acid, the extract phase is extremely viscous and difiicultly separable from the raflinate phase, while it be comes relatively fluid and quite readily separable when a larger proportion of the acid solution is used, such as substantially more than 10%, erably at least about 20%,

As has been indicated, the visbroken shale oil can be readily and effectively extracted by the spaans method of this invention. iOn the :other ihand, if it is desirable, 'the shale oil. .canibe distilled to recover a gas oil therefrom, representingrforfexample, all 'out about the first -5% overhead vand a residue amounting to about 520% ofthe shale oil, and containing at the same time .'gas oilconstituents formed by any thermal decomposition of heavier materials in the shale oil during the distillation, and the separated gas oil distillate can be eifectively extracted in 'accordance with this invention. Still further, yiffit is desired to treat the shale oil Without any` kind of 'heat treatment, other than that Which results 'from the retorting ci the oil shale inthe production of the shale oil, the extraction With formic acid can ib'e eiected in the presence cfa suitable diluerit, such as a light aromatic or aliphatic hydrocarbon, e. g., benzene and the like. Thus,'wherleas about one-half volume ofi90% 'formic acid per volume of visbrolren shale oil yields a railinate fhaving ra nitrogen content of about 0.5%, .the -vextraction or one volume of a Amixture of 80% untreated shale oil and by volume benzene, with onehalf volume of 90% formic acid yields a rainate having a nitrogen content of about 0.6% by Weight, based on the shale oil content thereof. The nitrogen contents of ranates obtained by extraction of a mixture of representative N-T-U shale oil and benzene with diiferent proportions of forrnc acid are shown in Table II.

TABLE II Vol. Ratio: Acid/ (Oil-l- Benzene Feed 4/100 8/1'00l 20/100 l0/100 Percent N in Ranate Y Layer 0. 9i 0. 73f 0. 63

It has been found that when the shale oil is subjected to a rst extraction with formic acid, and the raffinate oil from this irst extraction is treated With a further portion of forinic acid, a very stable emulsion is formed in the second treating operation, which emulsion is extremely diiiicult to break. However, it has been found that the emulsion is readily broken by admixing therewith a small proportion of extract recovered in the first extraction; the formation of the emulsion is essentially eliminated by adding a small portion of the first extract to vthe raflinate oil to be treated or to the formic acid to be used as treating agent, or to both, prior to said treatment. It appears that there is ypresent in the initial shale oil some material which is a very effective deinulsiiier for the oil-forrhc acid systern, or some material which forms With formic acid such a dernulsier, and that 'said material is readily and rather completely removed by treatment of the shale oil with a relatively small proportion of forrnic acid. Therefore, when the shale oil is treated with formic acid in a yplurality of stages, it is essential that each treating stage, after the iirst one in which the shale oil is rst extracted with the forrnic acid, be carried out in the presence cf an added portion of extract phase, or extracted material, from said ftlrst treating stage.

Economic application of the extraction operation of this invention depends on the recovery of the formic acid from 'both the raiilnate vand the extract phases. The raflinate phase contains only ra vrelatively small proportion of *':Eormicf acid, generally from about y0.5 Ytoabout `I2% :by Weight,

6 and the recovery Vof the `forniic Aacid therefrom is `readily accomplished `by distillation, 'after which the formic acid is returned for use in the extraction operation. On the other hand, the extract phase contains a relatively large rproportion of formic acid, as uncoinbined formic acid and as lcombined formio acid, generally :from about 40% to 'about 75% by Weight -of 'the fextract phase, While at the saine time containing extracted shale oil constituents'comprising lvaporizableconstituents ranginrT in vboiling points from relatively low values to relatively `high values, such as from about 150 C. to vabout 525 C. Representative formic acid rallnates and extractszof a visbrolren shale oil are characterized in Tables III and IV while the nitrogen and sulfur contents of liquid' product' fractions of visbroken' shale oil y"are shown hereinafter in Table V.

TABLE IIIv Extraction of thermally treated N-T-U shale oil Feeds: Wt. 4'HCOOIL' iiltcrecl liquid productfromthcrmally treated N-T-U oil.

Conditions: about 5 'minutes contacting-D-SO minutes settling;

room temperature.

Number of Stages 1 ,l 5 Oil Charged, parts by vo1 50 50 50 AcidCliargerl, parts by vol 25 50 y25 Composition of Raffinate Phase, parts by" weight:

` Total 529 28 "27. 3

Rafflnate:

Percent wt. 'of oil charged 61.5 59. 3 `60 N itrogencontent, percent Wt 0. 53 0 50 0.47 Gravity, API I 32.8

1 Counter-current.

TABLE IV Analyses of typical products from extraction of thermally treated N-T-U shale oil Ranatc Extract Nltrogen'Content, percent vvt 0. 4 4. 5 Sulfur Content, percent Wt 0. 7 0.4 OxygeniContent, 'percent wt. 0. 5 1.6 Formate, as percent Wt. HCOOIL. '0. 05 '70. 3 Gravity, API 33 f6. 7 SayboltfFurol Viscosity, sec. at 122 I 206 Distillatlon Analysis, percent Wt.:

.Gaslina'to 205 C 20.2 ca, 0.5 Lightv Gas Oil, 205-345 O 34. 2 25. 1 Heavy Gas Oil, S45-525 C 36. 8 41.8 Residue, 525 C... 8.8 y32.11 N Content of Guts, perce asoline 0.05 4 57 Light Gas Oil, 205-345 0.15 I Heavy Gas Oil, S45-525 0.52 4 60 Residue 1.59 4 50 S Content of Cutapcrcent W A.Gasoline 0.88 0.50 Light Gas Oil, 205-345 C 0.70 Heavy Gas Oil,.-345-525 AC 0. 64 0.44 "Residuen 0. 64 0. 74

It Will be Vseen from the data in Table lV that oxygen, as Well as nitrogen content, is lower in the raffinate than in unexti'acted shale oil, while sulfur is higher. Thus, forrnic acid selectively extracts both oxygen and nitrogen compounds, but not sulfur compounds. The API gravityof the railinate was-higher, and that of the 'extract Was lower-than that of thefeed. Thisappearsto be due to ithe gasoline fractionof the feedfcontaining relatively few oxygen and nitrogen compounds, thus being recovered almost exclusively in the rainnate, and to the aromatic character of the extracted material; that is, a high proportion of the nitrogen in shale oil exists as pyridine and pyrrole derivatives. The nitrogen content 'icreases with boiling point in the raffinate, but is essentially independent of boiling point in the extract.

In order to recover the formic acid from the extract phase by distillation, it is necessary to heat the mixture sufciently to decompose any addition or reaction products of the formic acid with shale oil components of the extract. However, it has been found that when the extract phase is heated alone to a temperature suniciently high to remove all of the formic acid from the shale oil constituents, there is a substantial loss of formic acid in the process, presumably attributable to thermal decomposition of formic cid content of some of the formates present at the high temperatures required for removal of the formic acid from the extract. It will be seen from Irable IV that the extract contains only a negligible `proportion of low boiling constituents up to 205 C. It has been found that the loss of the formic acid is essentially eliminated and that the formic acid is recoverable substantially free from shale oil extract components by distilling the extract phase in the presence of an added amount of a light hydrocarbon, preferably a low boiling hydrocarbon fraction obtained from the rafiinate produced in the ex traction, and particularly a light hydrocarbon fraction which is predominantly non-aromatic in character. The distillation of the extract phase in the presence of the light hydrocarbon is carried out so that the maximum temperature to which any appreciable amount of the formic acid or formate is subjected is about 165 C. The use oi a portion of the low boiling fraction recoverable from the raffinate phase or from the initial thermal treatment or the retorting step by fractional distillation has the advantage that it can be returned to the extraction zone, together with the formic acid recovered from the extract phase by its aid, with its concomitant viscosity-reducing effect on the shale oil. On the other hand, the relative immiscibility of 'the fcrmic acid and said light hydrocarbon maires it a simple matter to separate the two materia-ls by condensation and stratification.

Having discussed in detail various factors which affect the process of the present invention, the application of the process and the method whereby those factors are taken into consideration to effect the desired rennement of shale oil, will be better understood from a escription of the process which is made with speciic reference to the process scheme shown in the drawing.

A crude shale oil, such as an N-T-U retorted shale oil as produced at the Ride, Colorado, demn onstration plant or the U. S. Bureau of Mines, is fed by means of line ii to a pour-point and viscosity reducing operation such as is frequently applied to heavy crude or residual petroleum oils, as represented by thermal treatment in i2, wherein the crude shale oil is subjected to an elevated temperature appropriate to the operae tion, such as about 460 C., and in general, under superatmospheric pressure, for example, about 500 pounds per square inch, for sufficient time to effect a suitable reduction in the viscosity of the shale oil. A small proportion of gaseous product, for example of the order of about 5%, is separated by means of line i4 and a small proportion (Ob-3%) of residue is removed as indicated by line l5. It will be understood here that the remainder of the visbroken shale oil may be separated by distillation into Various fractions, such as a gasoline fraction, a light gas oil fraction, a heavy gas oil fraction and a residuuni fraction, such as indicated in the aforementioned Bureau of Mines Report, and the separate fractions may be treated sepa rately by the process of this invention. However, it has been found that thc total Visbroken oil, after separation of the gaseous product and the small proportion of residual material, is effectively treated by the process of the invention, and for purposes of illustration the description made with reference to the drawing is made in connection with such total visbrolzen oil. Typical data pertinent to the thermal treatment and the resulting products of N-T-U oil and gas-flow retorted oil are shown in |Table V.

TABLE V Thermal treatment of shale ozl to reduce pour nomi l Feed (l) (2) Temperature, oC.. y 450 460 Pressure, p. s. i. g 5l0i50 lic WHSV (Wt. Hourly space Vcl.):

prcheat. 1S 19 5.0 5. 4 Liquid 94. 0 92. 5 insoluble ResidueY 0. 4 2.7 Unaccounted for 0.6 0.

Properties of Liquid Product Percent wt. N l 2. 10 2. l Percent wt S 0.66 0.57 Percent wt. 1.03 1.2i Solids, gn/l0() 1n (centrifuge) O. 9 2. S Gravity, cAPI 24. 0 19. S Pour Point, F. 0 l0 Liquid Product Composition, percent wt. Feed:

Water 0. Al l). 5 Gasoline, to 13. 9 12.() Light Gas Oil, rOo- 2). 7 27. 2 Heavy Gas Oil, 34 35.1 33. 7 Residue, 525 C. 14. il 19. l

Total 94.0 l2 i Nitrogen and Sulfur Contents o Liquid i Product Fractions, percent wt.: N S N S Gasoline 0. 57 0. 70 O. CO 0. 67 Light Gas Gil... 1.0 0. 0i 2.0 0.6i Heavy Gas OiL. 2. 4 0. 52 2. 8 0.51 Residue 3.1i 0.55 3.8 0.50

liv-T-U ou.

2 Gas Flow Gil.

The visbroken oil produced by the thermal treatment in i2 is transferred by means of line I5 to the lower section of extractor ll, while formic acid is delivered to the upper end of extractor El, from suitable storage i9, by means of line 2Q. As shown, extractor il is an upright elongated Vessel which may suitably provided internally with any of the well-known means adapted to provide intimate contacting of counteriiowing streams of at least partially immiscible liquid substances, such as a suitable packing material, perforated plates, and the like. Instead of a single extractor as shown, the extractor may comprise a plurality of mixer-settler combinations arranged for countercurrent contacting of immiscible liquids in known manner. Also, it has been found that a single mixer-settler combination is effective to an unexpectedly great extent for the present purpose as will be seen from the results shown already in Table I. The shale oil is effectively treated in extractor I1 with from about one-half-'tc one volumeofI forinicfacid solution ofl from about 40 %v to, higher strength, preferably about 60% to. 90% strength iny aqueous solution, for each volume of the` oil. The temperature of the extraction is about ambient atmospheric temperature, although lower or higher temperatures mayy be4 utilized, just so that the temperature is not so` low as. t cause the viscosity of the materials to become too great for effective contacting and handling and the temperature is not so high as to. exceed the decomposition temperature of the formate salts; a temperature of about 50 C. has been found to be entirely satisfactory.. The. raffinate phase containingl a small proportion of dissolvedformic acid (see Table III) isf removed from extractor Il, byy means of line2 and the extract phase. is removed fromthe bottom of the extractor through line 22. AsA has been indicated before, the. shale oil may be admixed with a suitable diluent to reduce theviscosity of the system. Such a' diluent, for example, a light hydrocarbon, is suitably introduced by means of line 24 into line I6 carrying the shale oil. A particularly suitable diluent for this purpose is a portion of the light hydrocarbon fraction separated from the raflinate produced in the process, which is` suitably delivered to line 24 by means of lines 25 and 26. As has also been indicated before, when effecting the extraction in a plural stage operation, because ofy emulsion difficulties, it is desirable to make certain that at least a portion of material which is first extracted from the shale oil in its first contacting` with formic acid is present throughout the extracting zone. This is readily accomplished by Withdrawing a portion of the extract phase from line 22 and delivering it, as by line 21, to formic acid feed line il?. Alternatively, a portion of the extract phase can be Withdrawn ydirectly from the bottom of the extractor and returned to the top of the extractor; portions can be injected at different levels as indicated. Instead of utilizing a portion of the extract phase, which represents a preferred method, a portion of the recovered extract may be used instead with satisfactory results.

The ralinate phase in line 2i is delivered thereby to `a fractionator 30 for the recovery of the formic acid content thereof and of the oil constituents in one or more product fractions. Fracticnator Sii is of conventional design and cone acid storage i9. lit will be understood that all of the oil constituents of the raffinate phase can be recovered as a single bottoms product fraction from fractionator 30, and, if desired, the total oil product can be fractionated into various desired fractions in a separate fractional distillation operation.

The extract phase in line 22 is delivered by means thereof to a distilling 'fractionator 45, also of conventional design and construction, provided with suitable heating means, such as a heating coil 4b, overhead vapor line 47 with vapor condenser 48, overhead condensate collector 50 and reflux line l, and a bottoms drawoff line 52. A light hydrocarbon, preferably having an end boiling point not higher than about 150 C. and

preferably only about C. in orderl to avoid loss of formic acid by decomposition, and preferably being a portion of light hydrocarbons recovered Afrom the raflinate phase, such as separated from the overhead condensate in 35 and/or withdrawn by line 45 from fractionator 30, is delivered to fractionator 45, as by means of line 53 or lines 53r`r and 26. By distilling the extract phase in column 45, in the presence of the light hydrocarbon, thedistillation may be carried out while maintaining the temperature at any point therein Where formates are present at a temperature below about C. and the formic acid recovered, in` substantially 100% recovery in the overhead from the distillation. The lower the end boiling: pointl of the light hydrocarbonr the larger 1s the proportion thereof; which is required forthe recovery ofthe formicv acid; on the other hand.. thc licht hydrocarbon must have Sucicnt relative volatility to be readily distillable from thc extract, shale cil constituents- It is t0. be understood, of course, that the nature and the amount of light hydrocarbon which is used for this purpose is selected sok as to minimize any unnecessary retreatingr and handling of materials. It is a feature of the embodiment ofthe invention as shown in the drawing that the light hydrocarbon which is utilized in the recovery of the formic acid from'A the extract phase can be returned to the extractor, by means of lines 48, 2,5 and 24', said light hydrocarbon removed from the extractor in the raffinate phase and then recovered in fractionator 30 for rev-use in fractionator 45.

Instead cf recycling the fcrmic acid; and; light hydrocarbon as recovered in accumulator 50, to the extractor Il, the mixture may be stratied into formic acid and hydrocarbon phases, by the addition of water if necessary, to cause separation and stratication, the hydrocarbon returned directly to the fractionator 45, as by means of line 5l and/or line 48 and the formic acid recovered from separated aqueous formic acid, if a more concentrated formic acid solution is desired, as by Well known distillation methods.

The drawing, for simplicity, does not necessarily show all of the auxiliary equipment such as pumps, pipes, valves, outlets, inlets, tanks, heating lines, cooling lines, heat exchangers, temperature recording and control means, liquid level control means, and the like, which may be found to be desirable for the most effective operation of the process as applied to a given case under a selected set of operating conditions. The proper selection and placement of such equipment Will be evident to one skilled in the art in view of the description of the invention as made hereinbefore.

We claim as our invention:

l. The method for the production of a shale oil product having improved catalytic cracking properties from shale oil, which method comprises: (l.) intimately contacting the shale oil with from about two to about ten stoichiometrical proportions of formic acid for each atomic proportion of nitrogen present in said shale oil t0 reduce the nitrogen content of resulting railinate oil phase to a value of from about 0.4% to about 0.9% by weight; 2) separating resulting extract and raffinate phases; (3) recovering dissolved formic acid from the separated raflinate phase and returning it for further extraction use; and (4) recovering formic acid from the sepal rated extract phase by distillation in the presence of a light essentially non-aromatic hydrocarbon 11 under conditions to maintain formic acid and iormates the distilling zone at a temperature below about 155a C. and returning the recovered formic acid for further extraction use.

2. The method for the production of a shale oil product having improved catalytic cracking properties from shale oil, which method comprises: (l) subjecting crude shale oil to a mild thermal treatment to effect a substantial reduction in viscosity thereof With a minimum of thermal conversion; (2) intimately contacting the liquid product separable from the thermally treated shale oil with formic acid in excess of one stoichiometrical proportion thereof for each atomic proportion of nitrogen in the liquid product; (3) separating resulting raiiinate and extract phases; (4) separating formic acid and a light essentially non-aromatic hydrocarbon fraction from the raffinate phase; (5) recovering formic acid from the extract phase by distillation in the presence of a portion of the light hydrocarbon fraction separated from the raffinate phase; and (5) recycling formic acid recovered from the extract phase, and at least a portion of the light hydrocarbon fraction separated therewith, to extraction utility in step (2).

3. The method for the production of a shale oil product having improved catalytic cracking properties from shale oil, which method comprises: (1) intimately contacting the shale oil having a nitrogen content substantially greater than 1% by weight with formic acid in substantial excess of one stoichicmetrical proportion there of for each atomic proportion of nitrogen in the shale oil in the presence of a light hydrocarbon fraction as dened hereinafter; (2) separating resulting raiiinate and extract phases; (3) recovering dissolved formic acid from the separated raffinate phase and returning it for further extraction use; (4) recovering a light essentially non-aromatic hydrocarbon fraction from the raffinate cil and using a portion of it in extraction step (1) as defined hereinbefore; (5) recovering formic acid from the extract phase by distillation in the presence of another portion of said light hydrocarbon fraction separated from the raffina-te oil; and (6) recycling formic acid recovered from the extract phase, and at least a portion of the light hydrocarbon fraction separated therewith. to the extraction step (1).

4. The process according to claim 1, wherein the contacting of shale oil and formic acid in step (1) thereof is carried out in a multistage countercurrent contacting zone and effective demulsication conditions are maintained throughout the contacting Zone by introducing a small portion of separated extract phase obtained in subsequent step (3) to the contacting zone near the point of withdrawal of the raffinate phase therefrom.

ROBERT C. CASTNER. RAYMOND C. ARCHIBALD.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,912,349 Tuttle May 30, 1933 2,114,852 McKittrick Apr. 19, 1938 2,151,592 Ferris Mar. 21, 1939 2,263,176 Lazar et al Nov. 18, 1941 

1. THE METHOD FOR THE PRODUCTION OF A SHALE OIL PRODUCT HAVING IMPROVED CATALYTIC CRACKING PROPERTIES FROM SHALE OIL, WHICH METHOD COMPRISES: (1) INTIMATELY CONTACTING THE SHALE OIL WITH FROM ABOUT TWO TO ABOUT TEN STOICHIOMETRICAL PROPORTIONS OF FORMIC ACID FOR EACH ATOMIC PROPORTION OF NITROGEN PRESENT IN SAID SHALE OIL TO REDUCE THE NITROGEN CONTENT OF RESULTING RAFFINATE OIL PHASE TO A VALUE OF FROM ABOUT 0.4% TO ABOUT 0.9% BY WEIGHT; (2) SEPARATING RESULTING EXTRACT AND RAFFINATE PHASES; (3) RECOVERING DISSOLVED FORMIC ACID FROM THE SEPARATED RAFFINATE PHASE AND RETURNING IT FOR FURTHER EXTRACTION USE; AND (4) RECOVERING FORMIC ACID FROM THE SEPARATED EXTRACT PHASE BY DISTILLATION IN THE PRESENCE OF A LIGHT ESSENTIALLY NON-AROMATIC HYDROCARBON UNDER CONDITIONS TO MAINTAIN FORMIC ACID AND FORMATES IN THE DISTILLING ZONE A TEMPERATURE BELOW ABOUT 165% C. AND RETURNING THE RECOVERED FORMIC ACID FOR FURTHER EXTRACTION USE. 